Positive photoresist composition for liquid crystal device

ABSTRACT

The present invention relates to an LCD circuit photoresist composition for manufacturing fine circuit patterns on liquid crystal display circuits or semiconductor integrated circuits, and more particularly, and LCD circuit photoresist composition including (a) mixed polymer resins comprising a novolak resin with a molecular weight ranging from 3,000 to 9,000 and a fractionated novolak resin with a molecular weight ranging from 3,500 to 10,000; (b) a diazide-type photosensitive compound; (c) a photosensitizer; and (d) organic solvents. An LCD circuit photoresist composition of the present invention has excellent photosensitivity, retention ratio, resolution, contrast, heat resistance, adhesion, and stripper solubility, thus this photoresist composition can be easily applied to industrial work places for better working environments.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an LCD circuit photoresist compositionfor manufacturing fine circuit patterns on liquid crystal displaycircuits or semiconductor integrated circuits, and more particularly, toan LCD circuit photoresist composition including polymer resins thatproduce a photoresist layer, a photosensitive compound, and organicsolvents.

(b) Description of the Related Art

For fabricating fine circuit patterns on liquid crystal display circuitsor semiconductor integrated circuits, an LCD circuit photoresistcomposition is uniformly coated or applied on an insulating layer or aconductive metal layer of a substrate. The coated LCD circuitphotoresist composition is then exposed through a mask with some form,and the exposed substrate is developed to produce a desired pattern. Thepatterned photoresist coating is used as a mask to remove the insulatinglayer or the conductive metal layer, and the remaining photoresistcoating is removed to complete the fine pattern onto the substratesurface.

An LCD circuit photoresist composition is classified as a negative typeor a positive type depending on whether the exposed area or photoresistcoating becomes insoluble or soluble.

The important properties of LCD circuit photoresist compositions forcommercial use are photosensitivity, contrast, resolution, adhesion witha substrate, retention ratio, CD uniformity, and safety.

Photosensitivity refers to how fast an LCD circuit photoresist respondsto light. High photosensitivity is required, particularly inapplications where a number of exposures are performed to form multiplepatterns by a repeated process. Another example is when reduced light isused, like with the projection exposure techniques that use light passedthrough a series of lenses and monochromatic filters.

Improved photosensitivity is essential for a thin film transistor-LCD(TFT-LCD) that needs a long exposure time because of its bigger displaysize. Photosensitivity is inversely proportional to retention ratio, andthe retention ratio tends to reduce with higher photosensitivity.

Contrast refers to a ratio between the percentage of film loss in theexposed development area and the percentage of film loss on theunexposed area. Ordinarily, development of an exposed photoresist coatedsubstrate is continued until the coating on the exposed area iscompletely dissolved away. Thus, development contrast can be determinedsimply by measuring the percentage of film coating loss in the unexposedareas when the exposed coating areas are removed entirely.

Resolution refers to how finely a photoresist composition reproduces theimage of the mask utilized during exposure on the developed exposedspaces.

In many industrial applications, particularly in the manufacture of LCDsor semiconductor integrated circuits, an LCD circuit photoresist isrequired to provide a high degree of resolution for very fine lines andspace widths of 10 μm or less.

Adhesion with various substrates is one of the physical properties thatis required of an LCD circuit photoresist composition. Adhesionincreases selectivity by the existence of patterns on fine circuitsduring removing a conductive metal layer or an insulating layer by a wetetching process.

Generally, an LCD circuit photoresist composition includes polymerresins that produce a photoresist layer, a photosensitive compound, andsolvents. Various attempts have been previously made to improve thephotosensitivity, contrast, resolution, and the safety of LCD circuitphotoresist compositions.

As examples, U.S. Pat. No. 3,666,473 discloses a compound of a mixtureof two phenol formaldehyde novolak resins together with a typicalphotosensitive chemical; U.S. Pat. No. 4,115,128 discloses an organicacid cyclic anhydride added to a phenolic resin and a naphthoquinonediazide photosensitive chemical to increase photosensitivity; U.S. Pat.No. 4,550,069 discloses novolak resin, a o-quinone diazidephotosensitive chemical, and propylene glycol alkyl ether acetatesolvent being used for higher photosensitivity and for increased safety;and JP. Pat. No. 189,739 discloses a fractionating novolak resin forincreasing resolution and heat resistance. The above are well known inthe related arts.

Various solvents have been developed to improve physical properties ofan LCD circuit photoresist composition as well as work safety. Forexample, ethylene glycol mono ethyl ether acetate, propylene glycol monoethyl ether acetate, or ethyl lactate may be used as a solvent. However,there is still a need for LCD circuit photoresist compositions that aresuitable for various industrial applications, without sacrificing anyone of the properties of photosensitivity, retention ratio, contrast,resolution, solubility of polymer resin, adhesion with a substrate, orCD uniformity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a composition for anLCD circuit photoresist that exhibits high photosensitivity, retentionratio, contrast, resolution, CD uniformity, and adhesion with asubstrate, considering previous technical problems.

It is another object of the present invention to provide semiconductordevices using a photoresist composition as above.

In order to achieve these objects, the present invention provides an LCDcircuit photoresist composition including polymer resins, aphotosensitive chemical, a photosensitizer, and organic solvents, forforming a photoresist film comprising;

(a) mixed polymer resins comprising a novolak resin with a molecularweight ranging from 3,000 to 9,000 and a fractionated novolak resin witha molecular weight ranging from 3,500 to 10,000; (b) a diazide-typephotosensitive compound; (c) a photosensitizer; and (d) organicsolvents.

Furthermore, the present invention provides semiconductor devices usingsaid photoresist composition to be coated on a conductive metal layer oran insulating layer for forming a photoresist pattern by exposing anddeveloping steps and being removed by etching and stripping steps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be explained in detail.

The present invention relates to an LCD circuit photoresist compositionusing mixed polymer resins comprising a novolak resin and a fractionatednovolak resin, to improve physical properties such as photosensitivity,retention ratio, adhesion, etc. of the photoresist layer.

In the photoresist composition of the present invention, the (a) polymerresins include a novolak resin, and more preferably a mixture of anovolak resin and a fractionated novolak resin.

Said fractionation represents that the molecular weight of the polymerresin is arbitrarily controlled by adjusting the ratio among high,medium, or low molecular resins by using organic solvents.

The useful polymer resins employed in the photoresist composition of thepresent invention are well known in the related arts, however a novolakresin is also used in the present invention. The above novolak resin isa polymer produced by reacting an aromatic alcohol such as phenol, meta,and/or para cresol with formaldehyde.

The characteristic of the present Invention is that a fractionatednovolak resin produced by properly removing high, medium, and lowmolecular resins is used with a novolak resin for improving the functionof an LCD circuit photoresist.

The physical properties of the said novolak resin such asphotosensitivity, retention ratio etc. are different according to themixture ratio of meta/para cresols. The amount of meta cresol ispreferably 40 to 60 parts by weight, and that of para cresol is 40 to 60parts by weight. Meta cresol exceeding the above range brings highphotosensitivity that decreases the retention ratio, while para cresolexceeding the above range brings low photosensitivity. An LCD circuitphotoresist composition has a thermal flow because of the remaining heaton a pattern after a hard-bake process. The line width and gradient ofthe substrate after the hard-bake process can be controlled by eithermanipulating the ratio of meta/para cresols or manipulating themolecular weight of polymer resins, then treating it with vapor plasma.

The molecular weight of the novolak resin used in the present inventionpreferably ranges from 3,000 to 9,000, and the molecular weight of thefractionated novolak resin preferably ranges from 3,500 to 10,000. Themixture ratio of said novolak resin and fractionated novolak resin ispreferably 10 to 90 parts by weight: 90 to 10 parts by weight.

The content of polymer resins used in the present invention is 5 to 30wt %. If it is less than 5 wt %, the viscosity will be too low to coatwith a desired thickness, and if it becomes more than 30 wt %, theviscosity will be too high to coat uniformly.

The above (b) photosensitive compound is a diazide-type compound, suchas 2,3,4,-trihydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonateobtained by esterification of trihydroxybenzophenone and2-diazo-1-naphthol-5-sulfonic acid, and2,3,4,4′-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonateobtained by esterification of tetrahydroxybenzophenone and2-diazo-1-naphthol-5-sulfonic acid. Each of these can be usedindependently or in combination.

The diazide-type photosensitive compounds mentioned above are obtainedby reacting diazide-type compounds such as polyhydroxybenzophenone,1,2-naphthoquinonediazide, and 2-diazo-1-naphtho-5sulfonic acid.

Two methods for controlling photosensitivity by using a photosensitivecompound are diversifying the amount of photosensitive compound, andcontrolling the speed of esterification of 2,3,4-trihydroxybenzophenoneor 2,3,4,4′-tetrahydroxybenzophenone and 2-diazo-1-naphthol-5-sulfonicacid.

More preferably, the above photosensitive compound includes a mixture of2,3,4,4′-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonateand 2,3,4,-trihydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonate.The mixture ratio of these two compounds should be 30 to 70 parts byweight: 70 to 30 parts by weight.

The content of the above photosensitive compound is 2 to 10 wt %. If thecontent becomes less than 2 wt %, high photosensitivity decreases theretention ratio, and if it is more than 10 wt %, very lowphotosensitivity will be shown.

Furthermore, regarding the photoresist composition of the presentinvention, the (d) photosensitizer is used to increase photosensitivity.The above photosensitizer is preferably a polyhydroxy compound having 2to 7 phenol-type hydroxy groups with a molecular weight of below 1000.

Useful exemplary photosensitizers are shown below. It is preferable thatat least one is selected from the group consisting of 1 to 5.

wherein R is hydrogen, —(CH₃)_(n), —(CH₃CH₂)_(n), —(OH)_(n), or a phenylgroup, respectively or simultaneously (n is the integral number of 0 to5).

More preferable examples of the above photosensitizers are2,3,4-trihydroxybenzophenone, 2,3,4,4′-tetrahydroxybenzophenone,2,3,4,3′,4′,5′-hexahydroxybenzophenone, condensed acetone-pyrogarol,4,4-[1-[4-[1-(1,4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol(TPPA), 4,4-[2-hydroxyphenyl]methylene]bis[2,6-dimethylphenol](BI26X-SA),and others.

Optimal polyhydroxy compounds used above are4,4-[1-[4-[1-(1,4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol(TPPA), or 2,3,4,-tirhydroxybenzophenone.

The content of the above photosensitizer is preferably 0.1 to 10 wt %.

A photoresist composition of the present invention comprises (d) organicsolvents. Examples of organic solvents here are propylene glycol methylether acetate (hereinafter abbreviated to ‘PGMEA’) itself, or PGMEAmixed with ethyl lactate (EL), 2-methoxyethylacetate (MMP), propyleneglycol mono methyl ether (PGME), etc. However, PGMEA itself is best.

Additives such as colorants, dyes, anti-striation agents, plasticizers,adhesion promoters, speed enhancers, and surfactants may be added to theLCD circuit photoresist composition of the present invention. Coatingsuch additives on the substrate helps to improve each characterizedprocess performance.

The LCD circuit photoresist composition of the present invention is alsoused for manufacturing a semiconductor device, and the best example ofuse of such a semiconductor device is in an LCD circuit manufacturingprocess.

The photoresist composition of the present invention can be applied to asubstrate by such conventional methods as dipping, spraying, whirling,and spin coating. When spin coating, as an example, the photoresistsolution can be adjusted with respect to the percentage of solidcontents in the spinning process. Suitable substrates include silicon,aluminum, indium tin oxide (ITO), indium zinc oxide (IZO), molybdenum,silicon dioxide, doped silicon dioxide, silicon nitride, tantalum,copper, polysilicon, ceramics, and aluminum/copper mixtures or polymericresins.

The substrate coated with photoresist composition is heated at 80 to130° C. to perform soft baking. This step permits the evaporation of thesolvent without pyrolysis of a solid component in the photoresistcomposition. Generally, the concentration of the solvent is preferablyreduced to a minimum by the soft-baking step, and thus the soft-bakingstep is performed until the solvent is mostly evaporated and the LCDcircuit photoresist remains on the substrate in a thin coating layerwith a thickness of less than 2 μm.

Next, the substrate coated with the photoresist layer is selectivelyexposed to light, particularly ultraviolet light, using a suitable maskto obtain a desirable pattern. The exposed substrate is then dipped intoan aqueous alkaline developing solution until either the exposedphotoresist layer is entirely or almost dissolved. Suitable aqueousdeveloping solutions include an aqueous solution including alkalinehydroxides, ammonium hydroxide, or tetra methyl ammonium hydroxide(TMAH).

The substrate with the exposed photoresist removed is then taken outfrom the developing solution. The resulting substrate is heat-treated toimprove it and to increase the adhesion with the substrate and chemicalresistance of the photoresist layer. This process is called ahard-baking step. The hard-baking is done at a temperature below thesoftening point of the photoresist layer, preferably at about 90 to 140°C.

The developed substrate is treated with an etchant or with vapor plasmato etch the exposed portion, and the remaining photoresist protects thesubstrate regions which it covers. The photoresist layer is removed fromthe etched substrate using a stripper to complete the pattern on thesubstrate surface.

The following Examples further illustrate the present invention.However, the scope of the present invention is not limited thereto.

EXAMPLES Synthesis Example 1 Manufacturing Resins Before and AfterFractionation

(Synthesis of Meta/Para Novolak Resins)

45 g of meta cresol, 55 g of para cresol, 65 g of formaldehyde, and 0.5g of oxalic acid were added to an overhead agitator, and afteragitating, a homogenous mixture was synthesized. The reacted compositionwas heated at 95° C. for 4 hours. A recurrent condenser was replacedwith a distiller, then the reacted composition was evaporated at 110° C.for 2 hours. By vacuum evaporation at 180° C. for 2 hours, the monomerresidue was removed, and the melted novolak resin was cooled at roomtemperature. The number average molecular weight was measured by GPC,showing that a novolak resin with a molecular weight of 3500 wasobtained (the standard case of polystyrene).

(Fractionation of Novolak Resin)

100/30/100 grams of novolak resin obtained above/PGMEA/toluene wereadded together and agitated to synthesize a homogeneous mixture, whichwas then heated to 80° C. While agitating the reacted compound, 300 g oftoluene were slowly dripped into the compound, followed by cooling it to30° C. Only precipitated novolak resin was collected, and 120 g of PGMEAwas then added to the remaining compound and the temperature wasincreased to 80° C. Remaining toluene was removed by decompressiondistillation. The number average molecular weight was measured by GPC,showing that a fractionated novolak resin with a molecular weight of4000 was obtained.

Example 1

The above-obtained novolak resin and fractionated resin were used aspolymer resins in the ratio of 30:70.

An LCD photoresist composition was produced by adding 4 g of sensitizerand 20 g of resins (6 g of novolak resin and 14 g of fractionatedresin), 2 g of 2,3,4-trihydroxybenzophenone as a photosensitizer, and 74g of PGMEA (propylene glycol methyl ether acetate) as an organicsolvent, and then by agitating at 40 rpm at room temperature. A 5/5mixture of2,3,4,-trihydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonate and2,3,4,4-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonatewas used as the above sensitizer.

An LCD circuit photoresist composition manufactured above wasdrop-applied to 0.7 T (thickness: 0.7 mm) glass plates while rotatingthem at a constant rate. The resulting glass plates were heat-dried at115° C. for 90 seconds to obtain a photoresist film layer with athickness of 1.50 μm on the glass. The resulting glass plates wereexposed to ultraviolet light using a mask and then dipped into a 2.38%tetra methyl ammonium hydroxide aqueous solution for 60 seconds toremove the exposed portions and obtain photoresist patterns. Afterforming these patterns on the ITO glass, the glass was treated with anetchant, and the length of ITO unexposed by the etchant was measured.

Example 2

An LCD circuit photoresist composition was synthesized with the samemethod as in the Example 1, except a 5/5 mixture ratio (20 g of resin=10g of novolak resin+10 g of fractionated resin) was used.

Example 3

An LCD circuit photoresist composition was synthesized with the samemethod as in the Example 1, except a 70:30 mixture ratio (20 g ofresin=14 g of novolak resin+6 g of fractionated resin) was used.

Comparative Example 1

An LCD circuit photoresist composition was synthesized with the samemethod as in the Example 1, except only novolak resin was used.

Comparative Example 2

An LCD circuit photoresist composition was synthesized with the samemethod as in the Example 1, except only fractionated novolak resin wasused.

Experimental Example

Regarding the manufactured photoresist compositions from Examples 1 to 3and Comparative Examples 1 and 2, the physical properties were asdescribed in Table 1, found by the following methods.

A. Photosensitivity and Retention Ratiooriginal film thickness=thickness lost+thickness remainedretention ratio=(remaining thickness/original film thickness)

Photosensitivity was measured by calculating the energy needed to melt afilm according to exposing energy, under the same developing conditions.The soft-baking step was performed at 115° C., then the retention ratiowas measured after exposing and developing steps. The results regardingthe differences of thickness before and after developing are presentedin Table 1.

B. Heat Resistance

Tg (Glass Transition Temperature) is a method of expressing heatresistance measured by DSC.

C. Adhesion

The photoresist film on the ITO glass coated by an LCD circuitphotoresist composition was treated with an etchant to remove theexposed ITO after obtaining desired patterns (fine lines and widths)during the developing step. Adhesion was tested by measuring the etchedlength of ITO unexposed by an etchant. TABLE 1 Novolak Photosen-Remainder Heat Adhe- resin sitivity ratio resistance sion Section A¹ B¹Eth (mJ/cm²) (%) (° C.) (um) Example 1 30 70 6.5 92 115 0.72 Example 250 50 6.5 90 110 0.63 Example 3 70 30 6.5 88 106 0.54 Comp. 100 — 6.5 63102 0.67 Example 1 Comp. — 100 6.5 72 120 2.36 Example 2Note)¹novolak A resin:m-cresol/p-cresol = 4/6 mixture2. novolak B resin:m-cresol/p-cresol = 4/6 mixture fractionated

As shown in Table 1, the photoresist film photosensitive energy producedby photoresist compositions of Examples 1 to 3 had higher retentionratios compared with the photoresist film photosensitive energy usingtraditional photoresist compositions.

Furthermore, the photoresist layers produced by the LCD circuitphotoresist compositions of the present invention had higher retentionratios compared with the photoresist layers produced by traditionalphotoresist compositions. Therefore, the physical properties as aphotoresist layer of the present invention are excellent.

Furthermore, as shown in Table 1, the photoresist layers produced byphotoresist compositions of Examples 1 to 3 may bring improved adhesionand alteration of the pattern profile in the hard-baking step afterobtaining desired patterns (fine lines and widths) during the developingstep.

As described above, the LCD circuit photoresist compositions of thepresent invention have excellent photosensitivity, retention ratio,resolution, contrast, heat resistance, adhesion, and strippersolubility, thus these photoresist compositions can be easily applied toindustrial work places for better working environments.

1. An LCD circuit photoresist composition, comprising: (a) mixed polymerresins comprising a novolak resin with a molecular weight ranging from3,000 to 9,000 and a fractionated novolak resin with a molecular weightranging from 3,500 to 10,000; (b) a diazide-type photosensitivecompound; (c) a photosensitizer; and (d) organic solvents.
 2. The LCDcircuit photoresist composition according to claim 1, wherein thephotoresist composition comprises (a) 5 to 30 wt. % of the mixed polymerresins comprising the novolak resin with a molecular weight ranging from3,000 to 9,000 and the fractionated novolak resin with a molecularweight ranging from 3,500 to 10,000; (b) 2 to 10 wt. % of thediazide-type photosensitive compound; c) 0.1 to 10 wt. % of thephotosensitizer; and (d) 60 to 90 wt. % of organic solvents.
 3. The LCDcircuit photoresist composition according to claim 1, wherein themixture ratio of said novolak resin and fractionated novolak resin is 10to 90 parts by weight: 90 to 10 parts by weight.
 4. The LCD circuitphotoresist composition according to claim 1, wherein the diazide-typephotosensitive compound is a mixture of2,3,4,4′-tetrahydroxybenzophenone-1,2-naphtoquinonediazide-5-sulfonate,and 2,3,4,-trihydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonate.5. The LCD circuit photoresist composition according to claim 4, whereinthe mixture ratio of2,3,4,4′-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonateand 2,3,4,-trihydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonateis 30 to 70 parts by weight: 70 to 30 parts by weight.
 6. The LCDcircuit photoresist composition according to claim 1, wherein thephotosensitizer is at least one polyhydroxy compound selected from thegroup consisting of the following formulas 1, 2, 3, 4, and 5:

wherein R is hydrogen, —(CH₃)_(n), —(CH₃CH₂)_(n), —(OH)_(n), or a phenylgroup, respectively or simultaneously (n is an integral number of 0 to5).
 7. The LCD photoresist composition according to claim 6, wherein thepolyhydroxy compound is4,4-[1-[4-[1-(1,4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol(TPPA).
 8. The LCD photoresist composition according to claim 6, wherein thepolyhydroxy compound is 2,3,4,-trihydroxybenzophenone.
 9. The LCDcircuit photoresist composition according to claim 1, wherein theorganic solvent is at least one selected from the group consisting ofpropyleneglycolmethyletheracetate (PGMEA),propyleneglycolmethyletheracetate (PGMEA) and ethyllactate (EL),2-methoxyethylacetate (MMP), propyleneglycolmonomethylether (PGME), anda mixture thereof.
 10. Semiconductor devices using the photoresistcomposition according to claim 1, wherein the composition is coated on aconductive metal layer or an insulating layer for forming a photoresistpattern by exposing and developing steps, and being removed by etchingand stripping steps.